Free tool
Odds converter.
Decimal, fractional, implied probability — edit any one and the others follow. Exchanges speak decimal; your head probably still speaks fractions. This is the bridge.
Implied probability is the market's opinion, not the truth. Converting odds tells you what a price claims about the world. Whether that claim is wrong — and wrong enough to cover commission — is the whole game, and no converter answers it.
The worked example
Odds of 3.5 (5/2 in old money) imply 100 ÷ 3.5 = 28.6%. A £10 back returns £35 including stake — £25 profit. A £10 lay risks £25 to win £10. Sum every runner's implied probability in a market and you'll usually get just over 100% on an exchange, and well over it at a bookmaker: the gap is the margin you're paying, and it's the first number an honest operator checks.
Straight answers
How do you convert fractional odds to decimal?
Divide the fraction and add 1. So 5/2 = 2.5 + 1 = 3.5 in decimal. Decimal odds include your stake in the return, which is why exchanges use them: the maths of backing, laying and hedging is far cleaner.
How do you convert decimal odds to implied probability?
Implied probability = 100 ÷ decimal odds. Odds of 4.0 imply 25%. If your own estimate of the true chance is higher than the implied probability, the price is theoretically value — though having a better estimate than the market is the entire difficulty.
Why do implied probabilities in a market add up to more than 100%?
That excess is the overround — the margin built into the odds. Bookmaker books often run 105–120%; exchange markets are usually within a percent or two of 100% because traders compete the margin away, which is one honest reason exchange prices are generally fairer.
What are the common fractional odds in decimal?
Evens = 2.0, 6/4 = 2.5, 2/1 = 3.0, 5/2 = 3.5, 3/1 = 4.0, 9/2 = 5.5, 10/1 = 11.0. The pattern: numerator ÷ denominator + 1.
Reading a price is the alphabet. Reading a ladder is the language.
Practise on the free ladder trainer Free Chapter 0: the honest prospectus18+ · Education, not betting advice · No tips, no picks · BeGambleAware.org
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